Use `sort_unstable` rather than `sort` when creating listings

src/listing_stream.rs

@@ -45,7 +45,7 @@ impl<R: Read + Send + Seek> ListingStream<R> {
             let listing = listing?;
             list.push(listing);
         }
-        list.sort();
+        list.sort_unstable();
         Ok(list)
     }
 }